YC is trying to buy more pro rata with this deal, which is what a ton of YC founders complain about in later rounds. This will make things worse.
The criticism here is that you need to give up a higher % of your company down the road.
And getting the money now instead of later sounds to me like an amazing deal; you can continue for longer before you need to find those later investors, and by that time, you'll be worth more and get a better deal from them, and therefore also get a better deal from YC.
I don't know much about startup financing, but to my layman's eyes, this sounds like a good deal.